Mobile communications have become pervasive throughout modern society. Ready access to a mobile communication system is, for many, a practical necessity. A cellular, or cellular-like communication system is an exemplary mobile radio communication system whose availability is widespread throughout significant portions of the populated areas of the world.
A cellular communication system is constructed generally to be in conformity with operational requirements set forth in an operating specification promulgated by a standards-setting body. The operating specification, amongst other things, defines a radio air interface extending between communication stations, i.e., the network infrastructure and a mobile station, operable in the communication system. Regulatory bodies allocate portions of the electromagnetic spectrum. Different allocations are made for different types of systems, and different regulatory bodies regulate the use of the electromagnetic spectrum in different jurisdictions. And, operating standards associated with different communication systems define operating parameters including parameters associated with the frequencies upon which the radio air interface is defined.
While early implementations of mobile stations used to communicate in a cellular communication system were relatively bulky, and were relatively heavy, advancements in integrated-circuit, processing, and communication technologies have permitted the miniaturization of newer implementations of mobile stations. Mobile stations are now regularly of dimensions permitting their hand-carriage. And, increasingly, mobile stations are constructed to be operable in conformity with the operating requirements of more than one operating standard. Such a mobile station, referred to as a multi-mode mobile station, is capable of operation pursuant to a communication service by way of any communication system with which the multi-mode mobile station is operable.
Miniaturization of a mobile station provided as a result of the technological advancements noted-above has permitted the circuitry required for multi-mode mobile station to be housed in a housing of small dimension. Multi-mode mobile stations are, for example, sometimes of configurations permitting their carriage in a shirt pocket of the user. Miniaturization is provided, not only by reducing the physical dimensions of the circuit paths of the receive and transmit chains of the circuitry of the mobile station, but also through sharing of circuit components between circuit paths used for communications pursuant to the different communication systems.
Miniaturization of antenna elements presents unique challenges, particularly when the antenna element is to form part of a multi-mode mobile station, operable at disparate frequency bands. An antenna element is generally most effective in transducing signal energy when the transducer is of dimensions related to the wavelength of the signal energy that is to be transduced. For instance, antenna lengths corresponding to, or multiples of, one-quarter wavelengths of the signal energy that is to be transduced exhibit good antenna characteristics. When the mobile station forms a multi-mode mobile station that operates at different frequency bands, different sizes of antennas are needed to transduce the signal energy of the different frequencies and wavelengths. As the sizes of housings otherwise required to house the circuitry of a multi-mode mobile station continue to decrease, dimensional requirements of the antenna elements are sometimes a limiting factor limiting further miniaturization of a mobile station. Significant effort has therefore been exerted to construct an antenna, operable over multiple frequency bands, that is also of small dimension, thereby to permit its positioning within the housing of a mobile station.
A PIFA (Planar Inverted-F Antenna) is sometimes utilized to transduce signal energy at a mobile station. Generally, a PIFA is of compact size and is of a low profile while providing for transducing of signal energy at more than one frequency band. A problem typically exhibited with a PIFA, however, is that a PIFA generally exhibits pass bands of narrow bandwidths. A bandwidth of a PIFA is enhanced by configuring the PIFA together with a parasitic element. Such use of a parasitic element, however, increases the dimensions of the antenna. Additionally, tuning of the antenna becomes more difficult due to the additional resonant branches. Also, the branches sometimes introduce EMI (Electromagnetic Interference) that interferes with antenna operation.
An improved antenna structure, of small dimensions, and operable to transduce signal energy at multiple, disparate frequency bands is therefore needed.
It is in light of this background information related to radio communications that the significant improvements of the present invention have evolved.